An important change in the National Planning Policy Framework (NPPF) to remove the ‘town centre first’ principle from office developments has had little attention so far but is extremely serious in its implications – not least for the nation’s motorists who could be stuck in Bank Holiday-style jams every day of the working week if this leads to new business parks dotted along the motorways.

Our study, commissioned from the Metropolitan Transport Research Unit (MTRU), modelled new developments on the M1, and added just one new business park to each suitable junction between St Albans and Leeds.

Using a range of conservative assumptions (such as excluding all short trips), we found that just 34 business parks close to this 175-mile stretch of motorway would increase traffic by 16 per cent and nearly double the average level of delay – from 3.6 minutes to 6.4 minutes per 10 miles.

To put these figures in context, last August Bank Holiday Friday saw a 17% increase in traffic levels along the same part of the M1, so the level of extra traffic predicted by our model would effectively mean Bank Holiday conditions every working day.

The congestion caused would cost approximately £250 million a year in due to the extra delays alone, and the total extra journey time from Leeds to St Albans would be 50 minutes. With the government planning to spend billions on a high speed rail line to shave 36 minutes off a rail journey to Birmingham, it’s madness to be adding delays to hundreds of thousands of daily road journeys with badly thought through planning policy.

What needs to change in the NPPF for this not to happen? Key to the business park problem is that the ‘town centre first’ sequential test for commercial and office developments needs to be restored. However, these kinds of issues run right through the NPPF, which has downgraded a wide range of specific protections in the NPPF in favour of a “presumption of sustainable development”.

In transport, this means any congestion effects would need to be very severe for a development to be turned down. But the point our study illustrates very well is that lots of separate developments – each with measurable but not ‘extreme’ effects on congestion – could sail through this new planning regime and have a cumulative effect on the road network that was extremely serious indeed.

The same problem has also raised concerns about green field sites – see the National Trust’s reaction here. Opposition to the NPPF now threatens to move far beyond the range of civic, conservation and environmental groups who have spoken up so far. Today’s Telegraph includes both the director of the RAC foundation and a spokesman for the AA sharing our concerns about this new evidence of the dangers posed by the NPPF.

While we need to encourage new jobs and developments, we need make sure they go in the right places.

This is not about being against development, it is against a policy that will lead to empty sheds on bypasses, and in housing terms, potentially create the slums of the future.

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